1. Field of the Invention
The present invention concerns a miniaturized radio antenna element for use at VHF and UHF in particular, in other words in a frequency band extending from a hundred or so Megahertz up to a few Gigahertz. An antenna of this kind may be fitted to a radio communication satellite.
2. Description of the Prior Art
The earliest VHF and UHF antennas were wire antennas. At these relatively low frequencies the antenna has large overall dimensions which represents a serious weight and overall dimensions penalty in the case of a satellite. Furthermore, precisely because of these large overall dimensions, the antennas must be stowed in a folded configuration for storage and for launching the satellite and then deployed when the satellite is in its final orbit. This requires a complex, costly, bulky and heavy deployment mechanism and there is always the risk of failure when this mechanism is operated when the satellite has reached its orbit.
It is highly advantageous to miniaturize VHF and UHF antennas as much as possible and one way that springs to mind to achieve this is to use the currently fashionable technique of "patch" type printed circuit antennas comprising a conductive square separated from a ground plane by a thin insulative substrate whose permitivity is Er. The conductive square is deposited on the substrate by a conventional printed circuit technology and in a conventional implementation the side of the square has a length of approximately: EQU .lambda./2..sqroot.Er
where .lambda. is the wavelength transmitted or received by the printed circuit antenna.
In air and at the frequencies of relevance in the present context the dimensions of these antennas are still much too large.
The use of a substrate with a high dielectric constant Er, such as alumina, is one way to reduce the overall dimensions, but not to a sufficient degree. Also, a high permittivity represents a significant penalty in terms of the radiation properties of the resulting antenna, to the extent that a solution of this kind is in the final analysis somewhat suspect.
There are insulators with even higher permittivity, such as sintered ceramics. At present, however, it is not feasible to use such materials in an industrial environment. What is more, the radiation performance of such antennas would be even worse.
The invention is directed to alleviating these drawbacks.